The ultraviolet region (UV region) is a region of the electromagnetic spectrum adjacent to the low end of the visible spectrum. The UV region extends between 100-400-nm, and is divided into 3 sub regions: the UVA region (320-400-nm), the UVB region (280-320-nm), and the UVC region (100-280-nm).
In the last three decades, the levels of UV radiation that reach the earth have increased substantially due to the depletion of the ozone layer, caused by the release of various chemicals in the form of aerosols into the atmosphere.
In some parts of the world, the level of UV radiation has increased by 30-50%. The consequence of this process is a substantial increase in the danger of exposure to the sun's radiation.
It is believed, for example, that every 1% increase in the level of UV radiation corresponds to a 4% increase in the number of skin cancer cases. Indeed, according to medical statistics the number of skin cancer cases has increased by hundreds of percents in the last 20 years.
Of the three regions, the exposing to radiation in the UVB region is considered to be the most dangerous to human beings, since it causes several types of the must common cancer in human beings, i.e. skin cancer. One of the types of this cancer, namely melanoma, is lethal. In addition to the above, exposure to radiation in the UVB region can cause skin aging and is also harmful to eyes.
Radiation in the UVA region mainly causes damage, such as photo-aging, to the skin. Radiation in the UVC region does not penetrate the ozone layer, but is used in some industrial applications.
UV radiations also cause damage to agriculture crofts, plants, polymer and fabric made products.
On the other hand, artificial UV radiations is been used to cure printed ink, purify water, in semi conductors industry etc. In these cases there is a need to know the dose of exposure in order to prevent damage or to insure that the process will be successful.
Another application is using the irreversibility color change of the new device after exposure to UV from the sun or from artificial sources, in order to alert user if a package to which the device was attach/combine was open, or to confirm its originality by exposing the covered attached/combined device on the package to UV radiation and observe the irreversible color change.
In humans, UV radiation induces biological effects depending on the particular wavelength of the radiation. It is known to evaluate total biological or hazard weighted irradiation by multiplying the spectral irradiation at each wavelength by the biological or hazard weighted factor and then summation results of the multiplying over all the wavelengths.
Biological or hazard factors are obtained from the so-called action spectrum according to Environmental health criteria 160 “Ultraviolet radiation” issued by the World Health Organization, Geneva, 1994. An action spectrum is a graph of the reciprocal of the radiant exposure required to produce the given harmful effect at each wavelength. All the data in such graphs are normalized to the datum at the must efficacious wavelength. By summation of the biologically effective irradiation over the exposure period, the biologically effective radiant exposure (efficacy in J/m.sup.2) can be calculated.
The action spectrum graph for UV induced erythema was adopted worldwide by many organizations such as:
1. ACGIH (American Conference of Governmental Industrial Hygienists)
2. WHO (World Health Organization)
3. UNEP (United Nations Environment Program)
4. INIRC (International Non Ionizing Radiation Committee)
The action spectrum graph is a complex curve, obtained by statistical analysis of many research results establishing the minimum radiant exposure to the UV radiation at different wave lengths sufficient for causing erythema.
The most commonly used quantity of radiation associated with the erythemal potential due to exposure to UV radiation is the number of so-called minimum erythemal doses (MED) caused by the exposure. An MED is defined as the radiant exposure of the UV radiation that produces a just noticeable erythema on previously unexposed skin. The radiant exposure to monochromatic radiation at around 300 nm with the maximum spectral efficacy, which is required for erythema corresponds to approximately 200 to 2000 J/m. ^0.2 efficacy, depending on the skin type.
The skin reacts to radiation by changes in the melanin content. Subsequent to the change in the melanin content reddening occurs, and then soreness and signs of sun burning appear.
There exist 5 skin types that differ according to the color of human hair, eyes, and skin, and by their reaction to overexposure to UV radiation. The permissible time for exposure to UV radiation on a mid summer day changes from 15 minutes for skin type no. 1, to about 2 hours for skin type no. 5 (without using sun screen).
Most people are not aware of the danger that can arise even after limited exposure to UV radiation, because the dose is accumulated during the exposing for varying periods of time in a daily life routine. The first visible sign is usually sunburn, which might only become visible after a few hours. This means that the individual becomes aware of the danger only after the damage has already been done. It should be emphasized that skin cancer might even appear years later.
Unfortunately, most people routinely do not use sun screens unless they are on the beach or a trip. Even then, people usually do not use means of protection before they become exposed to the sun's radiation, and do not repeat applying sunscreen during exposure to the sun.
UV radiation level changes continuously, because of latitude, air pollution, season, clouds, and other factors. Therefore, it is very difficult to give accurate, reliable and timely warnings to the public about the UV radiation levels for specific location and day time. The only practical means that the public can use to defend itself is a personal measuring device.
Another problem is that the effectiveness of sunscreen lotions that decrease gradually due to perspiration, absorption and mechanical contact. The efficiency is also reducing as a function of the time pass since manufacturing. The public does not know how much to apply and when to reapply sunscreen. All sunscreens, which are transparent, block only part of the UV spectrum (until 360 nm), since there is also a pick in the UVA range (see the action spectrum graph), that is not blocked, and the user is left unprotected while assuming full protection.
A dosimeter was disclosed and described in U.S. Pat. No. 6,132,681 by the inventor of the present invention. The dosimeter disclosed in this application comprises a polymeric matrix with embedded therein a photochromic compound combine with UV absorber with effective gradient capable of changing its original color after exposure to UV radiation with efficacy corresponding to at least 1 MED.
There is a known-in-the-art disposable dosimeter for sun radiation as per Shiseido Co.'s U.S. Pat. No. 4,829,187. This dosimeter employs a photo sensitive composition consisting of a discoloring agent, a photo activator and a UV-ray absorber. The photo activator forms free radicals by the irradiation of UV rays and the discoloring agent exhibits a color change in the visible region of a spectrum through the action of free radicals and a UV-ray absorber. The disadvantage of this dosimeter is associated with the fact that its principle of operation, and therefore the compound employed therein, is neither suitable to measure the radiation dose which is equivalent to MED, nor is it selective to different types of the user's skin. The known dosimeter is designed in such a manner, that the amount of UV-radiation necessary for inducing the color change can be 1-100 J/cm.sup.2. These values are far away from the magnitude of UV-radiation corresponding to an MED, which is about 20 mJ/cm.sup.2 for skin type no. 2.
Also known is a method and device for monitoring UV radiation as disclosed in Cybrandian Ltd.'s U.S. Pat. No. 5,117,116. In the specification of this patent it is mentioned that to facilitate quantifying the minimum dose of UV radiation an individual can tolerate, the dose of UV radiation which induces reddening in the skin is referred to as the Minimum Erythemal Dose. This dosimeter employs a chemical compound capable of changing its color on being subjected to UV radiation reflected from the skin of the user. The principal disadvantage of this provision is associated with the fact that various types of skin in various conditions reflect differently and therefore cause enormous uncertainty in the determining of the actual dose of UV radiation to which the skin of an individual has been subjected irrespective of whether this dose is attributed as an MED or not. Furthermore, there is no mention in the specification of the above patent how the outside temperature might influence the performance of the chemical compound. Since for monitoring reflected radiation the dosimeter should be provided with a dedicated support means capable of directing the reflected radiation upon the chemical compound the dosimeter's construction is complicated and inconvenient to use.
There is known a sunburn dosimeter as disclosed in American Cyanamid Co.'s U.S. Pat. No. 3,903,243. The principle of operation of this dosimeter is based on comparing the color change of a test area bearing chemical compounds capable of changing their color depending on the cumulative exposure to UV radiation with a standard area. The standard area bears a chemical compound which changed its color after exposure to different predetermined quantities of sunburn radiation. Unfortunately, the chemical compounds employed in this dosimeter are not chosen depending on their sensibility to a radiation, the amount of which is equal to an MED. These compounds are chosen depending on their capability for coloration after exposure to radiation referred to arbitrary time units and assuming that there exists a linear relationship between the ultimate time of exposure and the skin type. This assumption is not correct from the medical point of view. It should also be mentioned that comparison of a test area with a standard area is inevitably subjective and therefore renders the dosimeter less accurate.
Furthermore, there is known an ultraviolet radiation dosimeter as per Trumble's U.S. Pat. No. 3,787,687. The principle of operation of this dosimeter is similar to the previously mentioned dosimeter and is based on the comparison of a standard color chart with the color of a chemical compound exposed to UV radiation. The chemical compounds employed in this dosimeter are not chosen deliberately depending on their sensitivity to an MED of radiation or to skin type.
Thus, one can see that despite the existence of various UV indicators and dosimeters there is still a need for a new, convenient, accurate and versatile measuring device which is both capable of giving timely and unequivocal and continues warning to the user about the amount of UV radiation to which he has been exposed and which also can be used for industrial and agriculture applications.